Rectifier



July 19, 1932. RElsMAN 1,868,175

RECTIFIER Filed Feb. 15, 1930 INVENTOR Ennl Riswmn Z BY / ATTORNEYS Patented July 19, 1932 UNITED STATES VPATEN'I? 1 OFFICE EIIIL REISMAN, OF BROOKLYN, NEW YORK, ASSIGNOB T0 TECHNIDYNE CORPORATION,

, or NEW YORK, N. Y., A. CORPORATION OF NEW YORK RECTIFIER Application filed Iebrhary 15, 1830. Serial No. 428,657.

This invention relates to rectifiers, and more particularly to rectifiers of thedry disc type and to a method of making the same.

Rectifiers of the dry type have been made by utilizing ametallic oxide. The most common exam leof such rectifiers is the copper oxide rectifier which is ordinarily made in the form of copper discs, one side of each of which is oxidized. The oxide is electronegative in character, and possesses a high specific resistance. It is in intimate contact with the copper by reason of having "been formed directly thereon and therefrom. The rectification takes place at the junction of the copper and the copper oxide of vthe disc.

Difliculty'is experienced when manufacturing such rectifiers in obtaining ood contact with the open side of the oxi e film or layer. This layer is high in resistance and has a rough surface with which it is diflicult to obtain intimate full surface contact.

As heretofore constructed, these rectifiers were assembled with soft metal, usually lead,

washers between the successive discs. The lead washer is clamped against the. copper oxide coating under ve great pressure, ordinarily of the magnitu e of 500 pounds per square inch or more. Under this pressure the relatively soft metal flows or is forced into the irregularities of the oxide surface, and in this manner a close and intimate contact may be obtained with a reasonably low contact resistance. Unfortunately, this con tact is satisfactory only when the unit is new,for after say several months of use or, in fact, even if the unit is not used, the contact resistance between the oxide and the soft metal increases rapidly, and this increase in contact resistance greatly decreases the efficiency of the rectifier. a

This increase in contact resistance seems to be due to a slow change in configuration or flow of thesoft metal washer under the great pressure to which it is subjected. In

- the heavy clamping pressure, and the resulting decrease in contact pressure increases the contact resistance. The primary object of the present invention is to overcome this difiiculty and to provide a low resistance contact which is not affected by the passage of time. I

The expansion and contraction of the rectifymg unit as it heats up in use and cools when not in use also serves to radually reduce the pressure between the soft metal washer and the oxide element, and this seems to be an additional important cause for increasingthe contactresistance, inasmuch as the effective area of contact is greatly reduced. The difficulty tends to be cumulative because for a given load or current the heat loss is increased when the resistance of the rectifier increases, and this in turn tends to further increase the growth of contact resistance, as well as to increase deterioration, and so to shorten the operating life of the rectifier'as. an eflicient unit. To limit the effect of this fault these rectifiers are usually, very conservatively rated as to output, but this, of course, is uneconomical in' the utilization of apparatus.

Another object of my invention is to overcome this additional difiiculty, and to provide an intimate contact with the surface of a dry rectifier which will be high in conductivity and permanent in value regardless of intermittent use.

A further object of my invention is to provide a method and means for obtaining such a contact without necessitating extreme pressure to maintain the same, thereby dispensing with the powerful clamping apparatus associated with such rectifiers.

To the accomplishment of the, foregoing and such other objects as will hereinafter appear, my invention consists in the method and rectifier elements and their relation one to the other as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing the single figure of which is a section taken in elevation through a group of rectifier elements embodyingamy invention.

eferring to the drawin the rectifier consists of one or more dry isc rectifying eleioo ments 2, each referably made of copper, the surface of at east one side of which is 0x1- dized to form a layer of copper ox de 4. The rectification takes place at the unction of the copper and the copper oxide, and electrical connection is made with the rectifymg element to the copper on one side and to the cop er oxide film on the other side. The ox1d e film or layer 4; possesses a high specific resistance and is rough, and it is therefore difiicult to obtain good electrical, contact therewith.

I have found that the various diflicultles attendant upon the use of separate metallic washers or discs between the rectifier elements for obtaining contactvwith the oxide film may be overcome by providing a contact surface which is deposited permanently and integrally on the oxide surface of the disc. Specifically, I paint the oxide surface of the disc with a metallic paint to form a conducting layer 6, which becomes an integral part of the dry disc, and which makes'intimate contact with the high resistance surface thereof regardless of the application of external pressure thereto.

The metal is preferably a non-oxidizing highly conductive metal such as silver, and the paint preferably consists of finely d1- vided silver particles suspended in a vehicle such as clear lacquer.

The paint may be coated on the oxide surface in any convenient manner as by brushing or spraying. It dries in a short time, say a few minutes, and in drying forms an adherent coating which because of its initial liquid hature penetrates and makes electrical contact with the entire area of the rough surface of the oxide. It flows into the various crevices and interstices of the oxide surface, thereby making excellent contact therewith, and when dry forms a coating which is tough and elastic so that it contacts permanently and integrally with the disc regardless of contraction and expansion thereof during use of the rectifier.

When the discs have been painted and dried it is simply necessary to assemble the desired number of discs in collateral relation to form the complete rectifier. Intermediate washers are dispensed with and the heavy assembly of bolts and nuts and end fittings and the like, ordinarily needed to obtain the necessary heavy and equalized pressure, may all be dispensed with. Simply one or several light screws or rods are needed to hold the discs together, inasmuch as no pressure or merely a negligible pressure is necessary.

The resulting rectifier is not'only more simple and more economical to construct than prior rectifiers, but is markedly superior from the electrical as well as from the mechanical viewpoint. This may be demonstrated by a fewspecific examples. A small low power disc rectifier of well known commercial make, rated for a half ampere direct current output, delivered only a third of an ampere current after less than ayear of use. This unit was dimantled and the oxide coated surface of the used discs were painted in accordance with the teachings of the present invention. The unit was reassembled without the original intermediate lead washers and without-the heavy bolts and nuts and end plates, the discs being held in assembled relation merely with light screws, resulting in a unit having less than ,half the weight of the original unit. The direct current output increased from a third ampere to twothirds of an ampere, so that the output of the rectifier Was doubled and brought to a value considerably higher than the normal rating and possible output of the rectifier when new. This latter point was checked by testing a new unit with lead washers clamped under full pressure, and the output was exactly the rated output, that is, a half ampere.

The used unit reconstructed and reassembled in accordance with my invention was additionally tested under overload conditions, and was found to operate satisfactorily over long periods of time even at 250 percent of the rated output. The temperature did not rise above 45 degrees 0., which was well within the allowable working temperature recommended by the manufacturer of the rectifier. Tests over long periods of time resulted in no discernible deterioration of the silver contact layer nor in any increase in contact resistance.

The method of constructing dry rectifiers in accordance with my invention and the numerous advantages of the resulting rectifiers will, it is thought, be apparent from the foregoing description. The complete assembled rectifier is greatly reduced in weight and size and cost of material. The contact resistance of the rectifier is reduced and'is kept constant regardless of time and regardless of intermittent use with accompanying temperature changes. Each disc is provided with a contact layer in an exceedingly simple and rapid manner, and this layer is permanently integral with the disc. The various discs may be assembled without appreciable pressure therebetween.

It will be appreciated that metallic paints other than the silver lacquer paint here mentioned may be employed and that silver, if

used, may be suspended in a vehicle other than lacquer. It will further be understood that my invention is applicable to dry rectifiers having a high resistance surface with which contact must be made other than the specific example of copper oxide here disclosed.

It will be apparent that while I have shown closed without departing from the spirit of the invention, defined in the following claims.

I claim: i 1. In the manufacture of a d rectifier 5 having rectifier elements each in'c uding an element of high specific resistance, the method of making contact with said elements which includes coating the same with a liquid paint comprising finely divided metallic particles previously suspended and difiused in a. liquid vehicle.

2. In the manufacture of a dr rectifier having rectifier elements each inc uding an electronegative element of high specific resistance, the method of makin intimate low resistance contact with said e ements which includes coating the same with a metallic paint comprising finely divided silver particles suspended in a binding vehicle.

3. In the manufacture of metallic oxide rectifiers the method of making contact with the oxide surface of the rectifier which includes coating the surface with a liquid paint comprising finelydivided metallic particles previously suspended and diffused in a liquid vehicle.

4. In the manufacture of copper oxide rectifiers the method of making contact with the copper oxide surface of the rectifier which includes coating the surface with a paint comprising finely divided silver particles suspended in a vehicle.

5. In the manufacture of copper oxide rectifiers the method of making intimate low resistance contact with the copper oxide surface of the rectifier which includes coating the surface with a metallic paint comprising finely divided silver particles suspended in lacquer.

6. A dry rectifier comprising rectifier elements each including an element of high specific resistance coated with a paint comprising finely divided metallic particles suspended in and held by a binding vehicle causing the metallic articles to conductively adhere to one anot er and to the element.

7. A dry rectifier having rectifier elements each including an electronegative element of high specific resistance coated with a metallic paint comprising finely divided silver particles suspended in a binding vehicle.

8. A metallic oxide rectifier including metallic discs each having an oxide surface coated with a paint comprisin finely divided metallic particles suspended in a vehicle.

9. A copper oxide rectifier including copper discs each having an oxide surface coated with a metallic paint comprising finely divlided silver particles suspended in a vehic e.

10. A copper oxide rectifier including copper discs each having an oxide surface coated with a metallic paint comprising finely divided silver particles suspended in lacquer.

11. A copper oxide rectifier comprising one or more discs each havin a layer of copper on one side, an adherent e astic la er including a mixture of finely divided silver particles and lacquer on the other side, and a layer .of copper oxide formed from the copper and located between it and the layer of silver.

Signed at New York, in the county of New York and State of New York, this 11th day of February, A. D. 1930.

EMIL REISMAN. 

